I just tried your code and found it to work well. Thanks.,Ray

See if you can put this into your Mathematica and run it without error.

Clear[t];
tau = .1;
V[t_] := 10 (1 - Exp[-0.1 t]);
dV = D[V[t], t];
v = 0;
points = Table[{time, v = v + dV /. t -> time}, {time, 0., 10, tau}];
ListPlot[points]

I may not have understood exactly the function you wished to create. If this code does not do what you need then perhaps you can modify it or you can try to explain your question in another way and I will see if I can modify this for you.

It seems like you are using several of your variable names for more than one thing. That may confuse Mathematica.

Can you see if you can understand this idea and perhaps adapt it to what you want to do?

Clear[t];(*Make sure t has no assigned value*)
V[t_] := 10 (1 - Exp[-0.1 t]);(*Define V function of t*)
dV = D[V[t], t];(*Define derivative of V at any t*)
v = 0;(*Start the iteration value with v=0*)
(*Now create a list of {time,v} values where t is replaced with time in dV*)
points = Table[{time, v = v + dV /. t -> time}, {time, 0., 10, tau}]

That tries to use the function V[t] for only that purpose, the derivative dV for only that purpose, the iteration time for only that purpose and the iteration value for only that purpose.

Then you can plot the result using this

ListPlot[points]

If I have misunderstood and you can explain then perhaps I will be able to correct this for you